1. Field of the Invention
The present invention relates to a method and system for evacuating a sample holder and, more particularly, to a method and system for evacuating a sample holder in such a way that a hermetic chamber can be connected to the inside of a goniometer under an evacuated state without replacing the insides of the goniometer and of the sample holder by an inert gas and that a sample can be inserted into the electron optical column of a microscope while reliably preventing exposure to the atmosphere.
2. Description of Related Art
A sample held on a sample holder is inserted into position within an electron microscope and irradiated with an electron beam. Then, charged particles and X-rays emanating from the sample are detected. Thus, the shape or composition of the sample can be estimated. In this situation, in a case where materials mainly containing a material such as a battery material that should be kept out of the atmosphere are analyzed, it is necessary that the sample holder be reliably inserted into the electron optical column of a microscope. Especially, in a case of a battery material that should be prevented from being exposed to the atmosphere, it is necessary to insert the sample into the electron optical column of the electron microscope in such a way that the sample is not exposed to the atmosphere.
FIGS. 6A-6H show a conventional sequence of steps for mounting a sample holder to a goniometer.
Referring to FIG. 6A, there are shown a glove box 1, a hermetic sample chamber 2 disposed in the box 1, a sample 3 placed at the front end of a rod 9, leaf springs 6 having front-end portions gripping the sample therebetween, a seal cap 4, a leak valve 5 mounted at one end of the seal cap 4, a knob 8, and seals 7. The rod 9 has a front-end portion on which the sample 3 is held. The sample 3 and the leaf springs 6 together form a sample holding portion. The sample holding portion and the rod 9 together form a sample holder. The inside of the glove box 1 is maintained in a vacuum or filled with an inert gas.
The rod 9 is used to transport the whole sample holding portion. The sample holder portion is transported into the hermetic chamber by manipulating the knob 8 attached to the rod 9. The sample is kept isolated and shut off from the outside atmosphere by sealing off the hermetic sample chamber 2 with a partition valve 11. The seal cap 4 seals the front end of the sample holder to thereby isolate the sample holding portion from the atmosphere if it is located at the front end of the holder. The seal cap 4 has the leak valve 5 mounted thereon and can place the inside of the cap 4 into communication with the outside atmosphere according to the need. When the microscope sample 3 is placed on the sample holding portion, the sample 3 is held by being sandwiched between the ancillary leaf springs 6.
The microscope sample 3 is held in the sample holding portion by the leaf springs 6 and thus placed in position within the glove box 1.
Referring to FIG. 6B, the seal cap 4 is attached at the front end of the holder, and the leak valve 5 of the cap 4 is closed. Under this condition, the partition valve 11 of the hermetic sample chamber 2 is kept open.
Referring to FIG. 6C, the sample holder is taken into the atmosphere out of the glove box 1 together with the whole seal cap 4. Then, the front-end portion of the sample is moved into the hermetic holder/sample chamber 2 with the knob 8. Subsequently, the partition valve 11 is closed to seal off the hermetic sample chamber 2. In particular, the sample 3 can be brought into the hermetic sample chamber 2 by moving a rod 15 holding the sample through the hermetic inside of the rod 9 to the right as viewed in the figure. As a result, the inside of the hermetic sample chamber 2 can hold the sample 3, and can be maintained as a vacuum or filled with an inert gas.
Referring to FIG. 6D, the leak valve 5 of the seal cap 4 is loosened such that the sample holder other than the hermetic sample chamber 2 is vented to the atmosphere. Then, the seal cap 4 is removed. Consequently, only the hermetic sample chamber 2 is held in a vacuum or inert gas ambient.
Referring to FIG. 6E, the sample holder is manually set into an electron microscope goniometer 15 and preliminary pumping is done, the goniometer 15 being mounted to the electron optical column 20 as shown.
Referring to FIG. 6F, the inside of the goniometer 15 is once vented and filled with nitrogen gas.
Referring to FIG. 6G, the partition valve 11 is opened and the sample 3 is moved into the front-end portion. Preliminary pumping is again performed, and the sample holder is inserted into the electron optical column 20. In this case, the sample 3 can pass through the goniometer 15.
Referring to FIG. 6H, the user performs a microscopic examination using the electron microscope. That is, an electron beam is directed at the sample 3. Secondary electrons, backscattered electrons emitted from the sample 3 or electrons transmitted through the sample 3 are detected.
FIG. 7 is a flowchart illustrating a pumping sequence for a conventional goniometer. This sequence is now described by referring also to FIGS. 6A-6H. First, all the partition valves are closed. Pumping of the goniometer 15 is started (S1). Then, pumping using an oil-sealed rotary pump and an oil diffusion pump is initiated (S2). The partition valve of the oil-sealed rotary pump is opened to start pumping using the rotary pump (S3). Then, a decision is made as to whether the degree of vacuum in the goniometer has reached a level at which pumping using the oil diffusion pump is needed (S4). If the level is not reached, the pumping using the oil-sealed rotary pump is continued.
When the degree of vacuum has reached a level at which pumping using the oil diffusion pump is required owing to the pumping using the oil-sealed rotary pump, the partition valve of the oil-sealed rotary pump is closed (S5). Then, the partition valve of the oil diffusion pump is opened (S6). A decision is made as to whether the degree of vacuum in the goniometer 15 has reached a level at which the pumping is complete (S7). If the pumping is not complete, the pumping using the oil diffusion pump is continued. If the degree of vacuum in the goniometer 15 has reached the level at which the pumping is complete, the pumping of the goniometer 15 is terminated (S8). At this stage, all the partition valves are closed.
One known apparatus of this type is described, for example, in JP-A-2010-61990 (paragraph 0025; FIGS. 4 and 5) and has a sample chamber in which a sample to be irradiated with an electron beam is disposed and gas inlet/exit piping including an inlet pipe for introducing gas into the sample chamber and an exit pipe for discharging gas from the sample chamber. One of the inlet and exit pipes surrounds the outer periphery of the other. The inlet and exit pipes have an increased cross section to increase the conductance for introduction and discharge of the gas.
A technique using a sealing block having a membrane-type gas ambient sample chamber is known and described, for example, in JP-A-2009-117196 (paragraph 0029; FIG. 1). The sealing block is supported by a pair of Y rotary shafts and bearings. The Y rotary shafts are located coaxially on the Y-axis. The sealing block consists of a gas supply tube forming a gas passage, a gas discharge tube, holes accepting the shafts, and a sample holder configured to hold the membrane-type gas ambient sample chamber. The sealing block can be hermetically tilted about the Y-axis.
The prior art techniques have the following problems.
1) Main battery materials to be analyzed are often crystalline. When they are observed with an electron microscope, accurate crystallographic adjustments are required. With the prior art techniques, tilting only about the X-axis is allowed. Therefore, it is impossible to tilt the sample exactly in the desired crystallographic orientation.
2) In the prior art techniques, the material of the front end of the sample holding portion is phosphor bronze that can be a background source when an energy dispersive X-ray analysis is performed. Therefore, undesired X-rays are produced, which is unsuited for energy dispersive X-ray analysis.
3) In the prior art techniques, when the insides of the goniometer and of the front-end portion of the holder are once replaced with an inert gas after the insides are pumped down, it is necessary to manipulate a switch plural times. During this time, there is the danger that an erroneous operation will take place, exposing the sample to the atmospheric gas temporarily.